Hello,
I would like to extract all images from a manga I bought recently, as you can see in the image. I can only export a single image at a time which is annoying. Is there a way to extract/export all images at once?

If the manga is in ePub format then I'd simply make a copy (Save to Disk if it is in a calibre library), change the extension from .epub to .zip, and then extract all of the files in the in the ZIP. You'll have all of the JPEGs along with, based on your screen shot, what seems like 12 xHTML files. Since you are working with a copy, you can simply delete any files other than the JPEGs and you can delete the ZIP file itself. Just be sure to do this to a copy and not the original.

In Calibre (not the editor):
Use the Unpack tool (you may want to add it to your toolbar) Keystroke "U"
the use the OS to copy the images to where you want Discard (Cancel), not Rebuild to exit the tool.